For example, cylinder pressure sensors supply valuable data about combustion in internal combustion engines. From their respective pressure profile it is possible for example to determine the quantity of energy converted over time and the combustion center of gravity of an internal combustion engine. As well as the crankshaft angle of the internal combustion engine, cylinder pressure also represents a central input variable for cycle calculations for the combustion process of the respective internal combustion engine. For example in the case of 4-stroke internal combustion engines the combustion process/cycle is divided into a high-pressure and a low-pressure loop. This is shown schematically in the p-V (pressure/volume) diagram in FIG. 2. There the high-pressure loop is marked AS and the low-pressure loop LWS. The high-pressure loop AS is made up of a work curve K1 for the expansion and/or combustion phase of the cycle and a sub-curve K2, which represents the compression phase of the cycle. The sub-curve K3 of the low-pressure loop represents the exhaust phase of the cycle. The sub-curve K4 of the low-pressure loop LWS describes the behavior of the 4-stroke internal combustion engine during its intake stroke. The high-pressure loop AS and the low-pressure loop LWS differ from one another essentially in pressure level. While the low-pressure loop LWS lies in a pressure range of around 1 bar, the high-pressure loop AS can in extremis go up to three-figure numerical values for the pressure p. This is the root of the measuring problem. Pressure sensors, embodied as analog sensors, supply an electrical signal proportional to the physical variable, i.e. the pressure. This electrical signal is converted by an electronic unit (in particular an instrument transformer) to a voltage signal and optionally amplified. The voltage signal emitted respectively by the pressure sensor then lies within a typical sensor output voltage range for example between 0 and 5 volts. This voltage signal is conducted from the pressure sensor to the engine control device and processed there by an A/D converter (analog-digital converter) in a manner appropriate for the processor. 8, 10 or 12 bit converters are generally used depending on the required accuracy. Higher resolution converters are rarely used in automotive engineering for EMC (electromagnetic compatibility) reasons. As the respective pressure sensor is expediently designed for a pressure range that can occur as a maximum in the respective cylinder of the internal combustion engine, low pressure values can only be reproduced approximately, even though a higher resolution could be supplied by the sensor element of the pressure sensor. For example with an 8-bit A/D converter, which can therefore display 356 measurement points, and an output voltage range between 0 and 5 volts for the pressure sensor, a resolution of 5 volts/256=19 mV results. In contrast the sensor element of the pressure sensor has a physically smallest resolution of around 1 mV for example. This means that the output signals from the pressure sensor can only be detected and/or registered from 19 mV due to the small number of measurement points for A/D conversion. The lower measuring range from 0 to 18 mV of the pressure sensor—corresponding in theory to 19 measurement values of the sensor element of the pressure sensor—remains unused despite higher resolution of the sensor element and cannot therefore be detected. In other words, it results in too low a resolution for the output signal of the cylinder pressure sensor.
One common option for improving A/D conversion would be to use a 10-bit converter instead of an 8-bit converter, in other words an A/D converter with more bits of conversion. In automotive engineering however—as described above—there are clear limits for the deployment of such measures. Another option would be to split the overall measuring range, for example into a low-pressure and a high-pressure range. For example the output voltage of the pressure sensor between 0 and 5 volts could be assigned a first measuring range between 0 and 2 bar and a second measuring range between 2 and 100 bar for the pressure in the respective cylinder. The pressure sensor would then have to be notified by a control signal from the engine controller or the engine control device which measuring range is currently active. Alternatively the pressure sensor could also switch independently between its various measuring ranges and notify the engine controller of the respectively activated measuring range via an additional control line. However this would be too complex in some practical motor engineering circumstances with regard to the signaling outlay between the internal combustion engine and the engine controller or control device. Such resolution and accuracy problems also occur in some instance with other measuring sensors, which are provided for the combustion process of an internal combustion engine.